Pipe bursting is a well known process that brings enormous potential for the efficient and unobtrusive replacement of buried pipelines. Currently the there are two widely used but separate systems used to accomplish pipe bursting. The choice of the system is most often dependent on the type of utility being upgraded.
Gravity sanitary sewer systems are made up of interconnected pipes buried at depths from (4) to (40) foot beneath the surface. These systems make use of ‘manholes’ to provide access for maintenance and cleaning of the interiors of the pipes. It is advantageous to minimize the damage and potential need for replacement of these manholes during the bursting operation. To do that requires practicing the method described in U.S. Pat. No. 6,299,382. That method calls for use of a pneumatic actuated tool, hydraulic winch with the guide cable passed through the existing pipe, and a front-mounted bursting head. Hence, primarily for that reason, most gravity sewer pipe bursting is done with pneumatic tools.
Potable water pipes are also widely in need of replacement. These systems, by the nature of the fact that they are pressure fed and therefore independent of the effects of gravity, tend to be buried at shallow depths in moderate climates. In addition, they do not have manholes, unlike the gravity sewer systems. For these reasons, water pipes are typically burst with a machine that requires an access pit at each end of the job. In the situation where there is no manhole present, having two access pits is not necessarily disadvantageous. The machine that fits this description is called a static system. Using significant hydraulically actuated force applied through a rod string, the tooling used on a static system splits the existing pipe and expands the surrounding soil. This style of bursting has four major components:
A. Tooling. This subsystem performs the function of cracking the pipe, expanding the adjacent soil with a conical form and a lastly provides a means of attachment of the product pipe to the rear of the tooling.
B. Rod String. The rods, threaded at each end, are engaged end to end into a string. This string transmits the pull force between the hydraulic pulling unit and the tooling.
C. Hydraulic power pack. This subsystem exists purely to provide pressurized hydraulic flow for operation of the pulling unit. The power pack may even be a hydraulic excavator configured to power auxiliary equipment as needed.
D. Downhole Unit. This is generally the most complex part of the machine; it entails the greatest amount of mechanism and complication of any of the four components. Hydraulic cylinders are employed to cyclically stroke a rod engagement system. The rod engagement may be through the threaded end, or by a mechanism that grips the rod outer surface or engages features on the outer surface. The engagement system must grip or engage the rod and apply thrust force in one direction, while sliding freely along the length of the rod in the opposite direction. This system must have the capability of being shifted relative to direction of operation so that rods may be added to, or removed from the string. An optional subsystem in downhole unit is a device to aid in the threading and unthreading of rods.
Two known pit launch static bursting machines are known commercially as the McLaughlin pit launch and the Vermeer PL8000. These are low force (10,0000 lb) pulling machines having a hole approximately 8″ in diameter in the front of the machine to accept small backreamers into the machine. When this is done, the vise floats (moves) with the spindle to allow the tooling to enter the machine. Since the pulling force was low, the hole did not present major problems with respect to soil entry or shoring area. With higher pulling forces, providing a hole in the front shore plate of the machine becomes problematic because soil will tend to enter the machine through the hole.